Plasma formation from micron-scale defects on ultra-pure aluminum rods*

The electrothermal instability (ETI) is a Joule heating-driven instability that can initiate in the solid state in magnetically driven fusion targets, specifically in current-carrying, fuel-filled metallic liners. ETI generates azimuthally correlated (striated) temperature and density perturbations, which may seed the magneto Rayleigh-Taylor (MRT) instability, limiting implosion uniformity and stagnation pressure. Previous experiments conducted on the ~ 1 MA Mykonos driver at Sandia National Laboratories have observed ETI growth from extremely smooth (Ra values <15nm), 99.999% pure aluminum rods in a z-pinch configuration by using ICCDs and a 12-frame imager to monitor overheating around characterized micron-scale "engineered" defects (ED) machined into the rod surface. New data comparing different ED size and orientation will be presented, revealing the surface structure of local overheating. "Cat eye" emission patterns, with bright emission spots above and below the ED, have been observed, as well as premature plasma filamentation sourced from ED. Experimental data has been compared with 3D-MHD simulations, denoting agreement in overheating surface structures including plasma filaments, peak intensities between ED pairs, and heating similarity for geometrically scaled defects.